Apparatus and methods are known for applying pressure-sensitive labels to a wide variety of articles. Most commonly in recent years, such labels have been supplied in the manner shown in FIGS. 1 and 2. An elongated carrier strip 10 having a centerline 12 is provided on one side with a surface having low affinity for the adhesive-backed side of a plurality of pressure-sensitive labels 14 whose display sides face outward from carrier strip 10. Labels 14 may be of practically any shape and are made of a moderately stiff material such as paper, to facilitate their ready removal from carrier strip 10, either by hand or by apparatus of the general types shown in FIGS. 3 to 5. In some instances, such as to provide tamper proof packaging for certain products, labels 14 may be provided with radially extending features such as outwardly extending tabs or arms 16 which can be folded over the sides of a cap on the article to prevent removal of the cap without destroying the tab.
Typically, such carrier strips and labels are wound into large rolls, though flat strips are also used. As shown schematically in FIG. 3, such a roll 18 is mounted for rotation so that strip 10, 12, 14 can be pulled around an idler roller 20 and then around the edge of a peeler plate 22. Because the adhesive backing on labels 14 has a low affinity for the surface of strip 10 and because labels 14 have a certain stiffness, the labels will release gradually and automatically from strip 10 as the strip passes around the edge of the peeler plate and will be presented essentially tangentially to the labeller head. Most commonly, the labels are applied directly to the article to be labelled as the labels leave the peeler plate, after which the labels may be tamped in place in the familiar manner. Another known apparatus for acquiring the label upon release is a reciprocating vacuum labeller head 24, whose undersurface is provide with ports connected to a source of subatmospheric pressure; so that, the label is sucked onto labeller head 24. Convenient to labeller head 24 is a conveyor or product nest 26 on which an article to be labelled is presented. The labeller head is then pressed against the article to apply the label and, in some instances, the vacuum is released and pressurized air is applied to push the label onto the article. From peeler plate 22, strip 10, 12 passes over a driven roller 30 and is rewound onto a roll 32.
FIG. 4 shows schematically yet another known type of labeller apparatus in which reciprocating labeller head 24 has been replaced by a rotating wheel or drum 34 whose periphery is provided with a plurality of circumferentially spaced vacuum ports or heads which move on a predetermined path to pull labels 14 one by one from strip 10, 12 and roll the labels onto articles 28 moving past on conveyor 26. Yet another known type of labeller apparatus, shown schematically in FIG. 5, is a sort of carousel 36 comprising an upper annular frame 38 and a plurality of vacuum heads 40 supported on frame 38 for reciprocation up and down by conventional means. A lower base 42 receives articles 28 from an adjacent feed wheel 44 and positions the articles below vacuum heads 40. As carousel 36 rotates, labels are fed to the vacuum heads moving along a predetermined path past peeler plate 22, after which the vacuum heads are lowered to press the labels against articles 28, which are then removed from base 42 by a discharge wheel 46.
In each of the known apparatus just mentioned, and also in the known apparatus shown schematically in FIGS. 22 to 24, several factors can prevent or considerably complicate accurate application of label 14 to article 28. As shown in FIGS. 1 and 2, the labels may not be centered relative to centerline 12 of strip 10; so that, they arrive at the vacuum labeller heads out of position for accurate application. The width of carrier strip 10 may vary from one roll 18 to another, which means that even if strip 10 is accurately guided at one edge across peeler plate 22, the transverse position of the labels reaching the vacuum labeller heads will vary from roll to roll. The strip 10, 12, 14 may in some labellers tend to wander or jitter transversely back and forth somewhat on peeler plate 22, causing the positions of successive labels to vary. Also, variations in the longitudinal position of the labels may be caused by typical variability in the label feed motor and in the take-up motor for the carrier strip, particularly when the labels are applied directly. Variations in the adhesive of the labels and in the vacuum applied can influence the position of the labels on the vacuum heads. Thus, a need has existed for an apparatus for applying such labels which can accommodate such malpositioning factors and still apply the labels quickly and with great accuracy to articles.